The present invention relates to a DC to DC converter, and more particularly to an DC to DC converter for operating in selectable input and output voltage modes.
FIG. 1 is a circuit diagram of a full-bridge phase-shifted soft-switching DC to DC converter according to the prior art. The DC voltage inputted into the input capacitor C11 is converted into a high frequency square-wave AC voltage through the switching devices S11 to S14 and sent to the primary winding of the transformer Tr. The secondary winding of the transformer Tr outputs two sets of square-wave alternative voltages having the same amplitudes, which are then rectified by the rectifier diode D11 and D12 and filtered by a filtering circuit composed of the inductor Lo and the capacitor C3 in series to obtain an output DC voltage. The two switching devices in the first arm of the full-bridge, i.e. S11 and S12, and the two switching devices in the second arm of the full-bridge, i.e. S13 and S14, are complementarily driven out of phase at 50% duty ratio of square-wave control signal. The output voltage is regulated by varying the phase shift of the control signal in the first arm and the control signal in the second arm. In addition, the operation efficiency of the converter could be increased by using the stored energy in the inductor Lk in the input loop of the transformer Tr to perform the soft turn-on of the switching devices S11 to S14.
FIG. 2 is a circuit diagram of an asymmetric half-bridge DC to DC converter according to the prior art. The DC voltage inputted into the input capacitor C21 is converted into a high frequency square-wave AC voltage through the switching devices S21 and S22. The DC components existing in the high frequency square-wave AC voltage is then filtered via the blocking capacitor Cb so as to send a square-wave AC voltage to the primary winding of the transformer Tr. The circuit loop in the secondary section of the transformer Tr includes rectifier diodes D21, D22, a inductor Lo and a capacitor C3, wherein the output DC voltage is regulated by varying the square-wave pulse time of the control signal of the switching devices S21, S22. In addition, the soft turn-on of the switching devices S21 and S22 is performed by using the stored energy in the inductor Lk in the input loop of the transformer Tr.
FIG. 3 is a circuit diagram of a full-bridge series-parallel resonant DC to DC converter according to the prior art. The DC voltage inputted into the capacitor C31 is converted into a high frequency square-wave AC voltage through the switching devices S31 to S34. The high frequency square-wave AC voltage is resonated by the series resonance circuit composed of a series resonant inductor Ls and a series resonant capacitor Cs and the parallel resonant circuit composed of a parallel resonant capacitor Cp and the input magnetizing inductor of the transformer Tr, thereby obtaining a sinusoidal alternative voltage as the input voltage of the transformer Tr. The circuit loop in the secondary section of the transformer Tr includes rectifier diodes D31, D32, a inductor Lo and a capacitor C3, wherein the output DC voltage is regulated by varying the switching frequency of the switching devices S31 to S34 to change the input voltage of the transformer Tr.
The DC-to-DC converters described in FIGS. 1 to 3 are suitable for the condition where the relative change of the input DC voltage and the output DC voltage is not wide. The operation performance and the converting efficiency of the DC to DC converter are decreased with the decreasing output voltage and the increasing input voltage. Furthermore, the DC to DC converter described above can be applied to the condition where only one input DC voltage is converted into one output DC voltage, which is costly and not environmentally friendly.
Therefore, the present invention provides a DC to DC converter for operating in selectable input and output modes for overcoming the problems described above.
It is an object of the present invention to provide a DC to DC converter capable of operating in selectable input voltage modes.
The DC to DC converter capable of operating in selectable input voltage modes according to the present invention includes a first input capacitor and a second input capacitor, a DC to AC circuit, a transformer, a rectifying circuit, a filtering capacitor, a first input DC voltage switching element and a second input DC voltage switching element.
In accordance with an aspect of the present invention, the first input capacitor and the second input capacitor is used for providing the at least one input DC voltage. The DC to AC circuit is connected with the first input capacitor and the second input capacitor for converting the input DC voltage to a high frequency first AC voltage and the DC to AC circuit includes four full-bridge switching devices. The transformer is used for converting the first AC voltage into a second AC voltage wherein the primary winding of the transformer is connected to the DC to AC circuit. The rectifying circuit is connected to the secondary winding of the transformer for rectifying the second AC voltage to the output DC voltage and the rectifying circuit includes four full-bridge rectifier diodes. The filtering capacitor is connected to the rectifying circuit for filtering the output DC voltage. The junction point of the first input DC voltage switching element is connected to the first input capacitor and the ends of the first input DC voltage switching element are connected with the second arm of the full-bridge switching devices. The junction point of the second input DC voltage switching element is connected to the second input capacitor and the ends of the second input DC voltage switching element are connected with the first arm of full-bridge switching devices.
Preferably, the first input capacitor is parallel with the first arm of the full-bridge switching devices and the second input capacitor is parallel with the second arm of the full-bridge switching devices.
Preferably, the rectifying circuit further comprises an output voltage switching element. The junction point of the output voltage switching element is connected to the filtering capacitor and the ends of the output voltage switching element are connected with the co-anode of the four full-bridge rectifier diodes and the central tapping head of the transformer.
Preferably, the at least one input DC voltage includes 200 V and 400 V.
It is another object of the present invention to provide a DC to DC converter for operating in selectable output voltage modes, which includes an input capacitor for providing the input DC voltage, a DC to AC circuit connected with the input capacitor for converting the input DC voltage to a high frequency first AC voltage wherein the DC to AC circuit comprises four full-bridge switching devices, a transformer for converting the first AC voltage into a second AC voltage wherein the primary winding of the transformer is connected to the DC to AC circuit, a rectifying circuit connected to the secondary winding of the transformer for rectifying the second AC voltage to the output DC voltage wherein the rectifying circuit comprises four full-bridge rectifier diodes, a filtering capacitor connected to the rectifying circuit for filtering the output DC voltage, and an output voltage switching element wherein the junction point of the output voltage switching element is connected to the filtering capacitor and the ends of the output voltage switching element are connected with the co-anode of the four full-bridge rectifier diodes and the central tapping head of the transformer.
Preferably, the output DC voltage modes are about 24 V and 48 V.
It is another object of the present invention to provide a DC to DC converter for operating in selectable input and output voltage modes, which includes a first input capacitor and a second input capacitor for providing the at least one input DC voltage, a DC to AC circuit connected with the first input capacitor and the second input capacitor for converting the input DC voltage to a high frequency first AC voltage wherein the DC to AC circuit comprises four full-bridge switching devices, a transformer for converting the first AC voltage into a second AC voltage wherein the primary winding of the transformer is connected to the DC to AC circuit, a rectifying circuit connected to the secondary winding of the transformer for rectifying the second AC voltage to the output DC voltage wherein the rectifying circuit comprises four fill-bridge rectifier diodes, a filtering capacitor connected to the rectifying circuit for filtering the output DC voltage, a first input DC voltage switching element wherein the junction point of the first input DC voltage switching element is connected to the first input capacitor and the ends of the first input DC voltage switching element are connected with the second arm, and a second input DC voltage switching element wherein the junction point of the second input DC voltage switching element is connected to the second input capacitor and the ends of the second input DC voltage switching element are connected with the first arm, and an output voltage switching element wherein the junction point of the output voltage switching element is connected to the filtering capacitor and the ends of the output voltage switching element are connected with the co-anode of the four full-bridge rectifier diodes and the central tapping head of the transformer.
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: